Boris Johnson says he is very likely to run for mayor of London again and it is "almost certainly the last big job I will do in British politics", remarks that appear to confound expectations that he is seeking a return to the frontline at Westminster. But Johnson also conceded that it would be "hubristic and mad" to formally announce his candidature three years before he is due to seek re-election.

In an interview with the Guardian to mark his first year in office, the Conservative mayor gave himself just "six and a half out of 10" for his mayoral performance to date. "If I think we are doing OK and I have a chance of being re-elected and people aren't too hacked off with me then yes, I would be absolutely crazy not to try for a second term. It's a wonderful job. It's almost certainly the last big job I will do in British politics."

The mayor hinted last week that he might stand down in 2012, fuelling speculation he was using the job as a springboard to return to national politics.

"I love my job, I'm almost certainly going to stand again. But I don't want to fire some sort of gun now and announce that I'm running again because now is not the time. I've only done a year. It would be hubristic and mad to announce now that I'm definitely standing again. I definitely want to be in a position where I could stand again," he told the Guardian. But he added: "In my heart, there might be something that happens in the next two years to make me think it's not a good idea."

Johnson denounced as "complete tripe" rumours that he and the Tory party leader, David Cameron, shared a mutual loathing. Both camps insist the two men speak at least once a week. Asked about suggestions in an updated biography that Johnson holds the Tory party leader in disdain, the mayor said: "It's simply not the case. We've always been very friendly and remain so."

The former journalist and MP for Henley, who confounded critics by wresting the mayoral crown from Ken Livingstone last May, admitted he found the job enjoyable but difficult.

"It is hard," he said. "Livingstone's right. I'm not a municipal politician by background or formation. It's just something I wanted to do and so there are bits of it that are technically quite new for me. Whole areas of planning law and that kind of thing which are taking a bit of beavering away at."

Johnson said he had backtracked on his demand for the mayor to be given the power to hire and fire the Metropolitan police chief, despite a rallying call at the Tory party conference last September when he claimed this was the only way to ensure that the mayor was held accountable for crime in London. Sir Ian Blair, the then police commissioner, felt he had no option but to resign when Johnson told him he had no confidence in him.

But the formal power to hire and fire rests with the home secretary, who will "have regard" to any recommendations made by the Metropolitan Police Authority (MPA).

Johnson said: "The whole experience over the last year has shown that one way or the other, de facto if not de jure, the mayor has very considerable powers of appointment and dismissal of the commissioner. That power is shared with the home secretary. As long as the role of the Met has a counter-terrorism dimension and various other national policing responsibilities it is right the home secretary should be involved, so my position has slightly evolved. I am more content than I was with the set-up simply because I have been able to satisfy London that the commissioner is accountable to the mayor."

The Met has come under fire over the video footage obtained by the Guardian that shows a police officer hitting newspaper seller Ian Tomlinson at the G20 demonstrations shortly before he died. But Johnson said he hoped that the "orgy of cop bashing" by sections of the media would soon "go away".

"Clearly people feel very sad about what happened to Ian Tomlinson, and very serious questions need to be asked, but people should not be blinded by that as to ignore the very successful work the police are doing on all sorts of fronts," he said. Johnson ruled out a separate review of public order tactics by the MPA, which has a strategic role over policing for London. "I think it would be quite wrong to pile review upon review," he said.

Johnson said his proudest achievement to date was safer public transport, following his decision to ban alcohol on tubes, buses and trams, and getting more police at transport hubs across the capital. A recently published annual survey of London showed an "upward kink" in the graph on people's feelings of safety on transport. "As a blushing beaming politician it was hard not to wonder whether that was attributable to the measures we put in," he said.

Johnson denied that he had failed to offer a clear vision for London. "A narrative evolves in the telling and you can't tell people the whole story in one year. Don't forget this was an institution that was run by a very different kind of political animal for a very long time. I think we've done a lot of very good things. I have a very, very clear idea in my head of where we want to go and the kind of London we want to create."

He admitted there had been "some effort" to "cohere" with the Conservative leadership and some "testing out" of policies, such as his waste-cutting efforts in the Greater London Authority budget. But he insisted: "London is not a petri dish into which various bacilli are being introduced by Tory ideologues. What we are doing is what we think is best for London."

Johnson insisted that he worked "very productively" with many Labour ministers. But he is facing a showdown with the Department for Environment, Food and Rural Affairs over his decision to scrap the western extension of the congestion charge (WEZ) and the low emission zone (LEZ) - both measures included in Defra's application to the EU commission for an extension on reaching its air quality limits.

"Defra haven't got a leg to stand on. They basically can't do that as long as they are still seriously proposing to build a third runway at Heathrow airport. It's insane. It massively adds to congestion in that area, and will hugely add to volumes of CO2 and other emissions in west London, far eclipsing the increases caused by what we have done with the LEZ or WEZ."

The strains and long days may explain why he fell asleep in the cinema last week, minutes after "laughing like a drain" at the film In the Loop, a satirical depiction of Whitehall life. "I could not believe it," he said. "In the middle of this incredibly funny, immensely topical, sharp, biting satire about all the subjects I'm interested in ... I just conked out."

Bumpy road: highs

May 2008 Ousts Ken Livingstone. Announces alcohol ban on tubes, buses and trams.September Cheered at Tory conference for announcing a freeze on the GLA's share of council tax.October Forces Sir Ian Blair to step down as head of Met.February 2009 Promises to stump up a third of £60m needed for 25,000 charging points for electric cars. April Ends first year with an approval rating of +25, according to YouGov.

Bumpy road: lows

May Seen cycling through six red lights, one pedestrian crossing and on pavement. June Aide James McGrath forced to resign - first of four advisers to leave.September Announces 6% rise in tube and bus fares. November Shelves £3.5bn of transport schemes. Scraps western extension of congestion charge.